JP4845919B2 - Image forming apparatus - Google Patents

Description

The present invention relates to image imaging apparatus, and more particularly, relates to suitable images forming apparatus when applied to a an electrophotographic apparatus, electrostatic recording apparatus provided with a heating device for a belt heating type as an image heating apparatus.

  Conventionally, there is an image heating device (fixing device) mounted on an image forming apparatus. In the conventional example, for convenience, an image heating apparatus (fixing apparatus) that is mounted on an image forming apparatus such as a copying machine or a printer and that heats and fixes a toner image on a recording material will be described as an example.

  In an image forming apparatus such as a copying machine or a printer, an image is formed and supported on a recording material by a transfer method or a direct method by an appropriate image forming process means such as an electrophotographic process, an electrostatic recording process, or a magnetic recording process. Yes. The recording material includes a transfer material sheet, an electrofax sheet, an electrostatic recording paper, an OHP sheet, a printing paper, a format paper, and the like. In this type of image forming apparatus, a heat roller type apparatus is used as a fixing apparatus that heats and fixes an unfixed image (toner image) of target image information formed and supported on a recording material as a fixed image on the recording material surface. Was widely used. Recently, belt heating systems have been put into practical use from the viewpoint of quick start and energy saving. An electromagnetic induction heating type apparatus has also been proposed. Hereinafter, various fixing devices in the image forming apparatus will be described.

(A) Heat roller type fixing device A heat roller type fixing device is basically composed of a pressure roller pair of a fixing roller (heating roller) and a pressure roller. The roller pair is rotated, and a recording material on which an unfixed toner image to be image-fixed is formed and supported is introduced into a fixing nip portion that is a mutual pressure contact portion of the roller pair, and is nipped and conveyed. The unfixed toner image (unfixed image) is fixed to the surface of the recording material by heat and pressure by the heat of the fixing roller and the pressure applied to the fixing nip.

  In general, the fixing roller has a hollow metal roller made of aluminum as a base body (core metal), and a halogen lamp as a heat source is inserted into the inner space thereof. The fixing roller is heated by the heat generated by the halogen lamp, and the temperature of the fixing roller is controlled by controlling the energization of the halogen lamp so that the outer peripheral surface is maintained at a predetermined fixing temperature.

  In particular, as a fixing device of an image forming apparatus that performs full-color image formation that requires a capability of sufficiently melting and mixing a toner image of a maximum of four layers, a core metal of a fixing roller has a high heat capacity. ing. In addition, a rubber elastic layer for wrapping the toner image around the core metal and melting it uniformly is provided, and the toner image is heated through the rubber elastic layer. There is also a configuration in which a heat source is also provided in the pressure roller so that the pressure roller is also heated and temperature-controlled.

  However, the heat roller type fixing device has the following problems even when the image forming apparatus is turned on and the energization of the halogen lamp, which is the heat source of the fixing device, is started. That is, the heat capacity of the fixing roller is large, and a considerable waiting time (wait time) is required until the fixing roller or the like is cooled down to rise to a predetermined fixing temperature, and the quick start property is lacking. In addition, it is necessary to energize the halogen lamp and maintain the fixing roller at a predetermined temperature control state so that the image forming operation can be executed at any time even when the image forming apparatus is in a standby state (non-image output). There were problems such as high power consumption.

  Further, in the case of using a fixing roller having a particularly large heat capacity, such as the fixing device of the above-described full-color image forming apparatus, a delay occurs in the temperature control and the temperature increase on the surface of the fixing roller. Problems such as offset occurred.

(B) Film Heating Fixing Device Various techniques have been proposed for film heating fixing devices (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4).

  That is, a nip portion is formed by sandwiching a heat resistant film (fixing film) between a ceramic heater as a heating body and a pressure roller as a pressure member. A recording material on which an unfixed toner image to be image-fixed is formed and supported is introduced between the film in the nip portion and the pressure roller, and is nipped and conveyed together with the film, so that the ceramic heater of the nip portion is conveyed. Heat is applied to the recording material through the film. Then, the unfixed toner image is fixed to the surface of the recording material by heat and pressure with the applied pressure of the nip portion.

  This film heating type fixing device can constitute an on-demand type device using a ceramic heater and a low heat capacity member as a film. Only when the image forming apparatus performs image formation, the ceramic heater as a heat source may be energized to generate heat at a predetermined fixing temperature. Therefore, there are advantages such as a short waiting time from the power-on of the image forming apparatus to an image forming executable state (quick start property) and significantly low power consumption during standby (power saving). However, a full-color image forming apparatus that requires a large amount of heat or a fixing device for a high-speed model has a problem in terms of heat.

(C) Electromagnetic Induction Heating Type Fixing Device Various techniques have been proposed for electromagnetic induction heating type fixing devices (see, for example, Patent Document 5). Patent Document 5 discloses an induction heating fixing device that induces a current in a fixing roller by magnetic flux and generates heat by Joule heat. This makes it possible to directly heat the fixing roller by using the generation of induced current, and achieves a fixing process that is more efficient than a heat roller type fixing device using a halogen lamp as a heat source.

  However, since the energy of the alternating magnetic flux generated by the exciting coil as the magnetic field generating means is used for raising the temperature of the entire fixing roller, there is a problem that the heat dissipation loss is large, the density of the fixing energy with respect to the input energy is low, and the efficiency is not good. .

  Therefore, in order to obtain energy that acts on fixing at high density, the excitation coil is brought close to the fixing roller, which is a heating element, or the alternating magnetic flux distribution of the excitation coil is concentrated in the vicinity of the fixing nip portion to achieve high efficiency fixing. A device was devised.

  For the sake of convenience, with reference to FIG. 2 used in an embodiment of the present invention to be described later, the schematic configuration of an example of an electromagnetic induction heating type fixing device that improves the efficiency by concentrating the alternating magnetic flux distribution of the exciting coil on the fixing nip will be described. While explaining. In the figure, reference numeral 10 denotes a cylindrical fixing film as an electromagnetic induction heat generating rotating body having an electromagnetic induction heat generating layer (conductor layer, magnetic layer, resistor layer). Reference numeral 16 denotes a saddle-shaped film guide member having a substantially semicircular arc shape in cross section, and the cylindrical fixing film 10 is loosely fitted outside the film guide member 16. Reference numeral 15 denotes a magnetic field generating means disposed inside the film guide member 16, which includes an exciting coil 18 and an E-type magnetic core (core material) 17. Reference numeral 30 denotes an elastic pressure roller. The fixing film 10 is sandwiched between the lower surface of the film guide member 16 so as to form a fixing nip portion N having a predetermined width with a predetermined pressing force, and are pressed against each other. The magnetic core 17 of the magnetic field generating means 15 is disposed so as to correspond to the fixing nip portion N.

  The pressure roller 30 is rotationally driven in the counterclockwise direction indicated by the arrow by the driving means M. A rotational force acts on the fixing film 10 by a frictional force between the pressure roller 30 and the outer surface of the fixing film 10 by the rotation driving of the pressure roller 30. While the inner surface of the fixing film 10 slides in close contact with the lower surface of the film guide member 16 in the fixing nip portion N, the film guide has a peripheral speed substantially corresponding to the rotational peripheral speed of the pressure roller 30 in the clockwise direction indicated by the arrow. The outer periphery of the member 16 is rotated (pressure roller driving method). The film guide member 16 is used to pressurize the fixing nip N, support the exciting coil 18 and the magnetic core 17 as the magnetic field generating means 15, support the fixing film 10, and transport stability when the fixing film 10 rotates. To play a role. The film guide member 16 is an insulating member that does not hinder the passage of magnetic flux, and a material that can withstand a high load is used.

  The excitation coil 18 generates an alternating magnetic flux by an alternating current supplied from an excitation circuit (not shown). The alternating magnetic flux is intensively distributed in the fixing nip portion N by the E-type magnetic core 17 corresponding to the position of the fixing nip portion N, and the alternating magnetic flux generates electromagnetic induction heat of the fixing film 10 in the fixing nip portion N. Generate eddy currents in the layer. This eddy current generates Joule heat in the electromagnetic induction heating layer due to the specific resistance of the electromagnetic induction heating layer. The electromagnetic induction heat generation of the fixing film 10 is concentrated in the fixing nip portion N where the alternating magnetic flux is concentrated, and the fixing nip portion N is heated with high efficiency. The temperature of the fixing nip portion N is controlled so that a predetermined temperature is maintained by controlling the current supply to the exciting coil 18 by a temperature control system including a temperature detection unit (not shown).

Thus, the pressure roller 30 is driven to rotate, and accordingly, the cylindrical fixing film 10 rotates around the film guide member 16. In the state where the electromagnetic induction heat generation of the fixing film 10 is performed by supplying power from the excitation circuit to the excitation coil 18 and the fixing nip portion N rises to a predetermined temperature and is adjusted in temperature as described above, the following operation is performed. A recording material P on which an unfixed toner image t conveyed from an image forming means (not shown) is formed has an image surface facing upward between the fixing film 10 and the pressure roller 30 in the fixing nip N, that is, the fixing film. Introduced opposite the surface. In the fixing nip portion N, the image surface is in close contact with the outer surface of the fixing film 10, and the fixing nip portion N is nipped and conveyed together with the fixing film 10. In the process in which the recording material P is nipped and conveyed through the fixing nip N together with the fixing film 10, the unfixed toner image t on the recording material P is heated and fixed by being heated by electromagnetic induction heat generation of the fixing film 10. Is done. When the recording material P passes through the fixing nip portion N, it is separated from the outer surface of the rotating fixing film 10 and discharged and conveyed.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 Japanese Utility Model Publication No. 51-109739

  However, the conventional configuration described above has the following problems. When power is supplied to the fixing device in a state where the induction heating coil (excitation coil) and the fixing film are cooled, the lead wire constituting the induction heating coil and the resistance value of the metal constituting the load sleeve are used. Since the skin resistance is small, a large current flows in the circuit. For this reason, a switch element having a large current must be used, leading to a cost increase. In addition, as the temperature of the induction heating coil and the sleeve rises, it becomes difficult for the current to flow due to an increase in resistance accompanying the temperature rise, and the current decreases. There was a problem that the raising time was slow.

The present invention has been made in view of the above points, and by keeping the average current flowing in the magnetic field generating means constant, it is possible to suppress fluctuations in the maximum power even when the power supply voltage fluctuates, thereby generating magnetic fields. An object of the present invention is to provide an image forming apparatus capable of increasing an allowable voltage fluctuation range of an AC input power supply for supplying power to the means .

To achieve the above object, the present invention provides a magnetic field generating means for generating a magnetic field, a power supply means for supplying power to the magnetic field generating means connected to an AC input power source, and a magnetic field generated from the magnetic field generating means. An electromagnetic induction heating member that generates electromagnetic induction heat by operation; a temperature detection unit that detects a temperature of the electromagnetic induction heating member; and generation of the magnetic field from the power supply unit so that the detected temperature of the temperature detection unit becomes a target temperature. An electromagnetic induction heating type heating device having a control means for controlling the power supplied to the means, wherein the heating device heat-fixes an unfixed image on the material to be heated. Current control means for detecting the supplied current; and filtering means for detecting the current detected by the current detection means as an average current value. , Said to linearly vary the magnetic field the maximum power that can be supplied to generating means with respect to variation in the voltage of the AC input power source, the magnetic field generating said average current value detected by the filtering means so as to maintain a constant Limiting the maximum current flowing through the means, and controlling the power supplied from the power supply means to the magnetic field generation means within a range not exceeding the maximum power so that the detected temperature becomes the target temperature. To do.

According to the present invention, the power supply means limits the maximum current flowing through the magnetic field generation means so as to keep the detected average current value constant, and does not exceed the maximum power so that the detected temperature becomes the target temperature. To control the power supplied to the magnetic field generating means. Thereby, the average current flowing through the magnetic field generating means can be kept constant, and fluctuations in the maximum power can be suppressed even when the power supply voltage fluctuates. Furthermore, since the maximum power that can be supplied to the magnetic field generating means increases linearly with respect to the voltage of the AC input power supply, the allowable voltage fluctuation range of the AC input power supply is increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
In the first embodiment of the present invention, a fixing device (heating device) mounted on an image forming apparatus, an exciting coil, a fixing belt, a high-frequency inverter device, a current detection unit, temperature control, and voltage dependence of maximum power in the fixing device. Each item of safety and safety device will be explained.

<Fixing device (heating device)>
The fixing device according to the first embodiment of the present invention is an electromagnetic induction heating type device. FIG. 2 is a block diagram showing the cross-sectional structure of the main part of the fixing device 100 according to the first embodiment of the present invention, FIG. 3 is a block diagram showing the front structure of the main part of the fixing device 100, and FIG. 2 is a configuration diagram showing a longitudinal sectional structure of a main part of the apparatus 100. FIG. In addition, description of the part which is common in the part demonstrated with the said prior art example is abbreviate | omitted or simplified.

The configuration of the main part of the fixing device 100 will be described in detail. The magnetic field generating means includes magnetic cores 17a, 17b and 17c and an excitation coil 18. The magnetic cores 17a · 17b · 17c are members of high magnetic permeability may material used in the transformer core such ferrite or permalloy is more preferably to use a small ferrite loss even higher 100 k Hz. In the excitation coil 18, an excitation circuit 27 (see FIG. 5) is connected to the power feeding units 18a and 18b. The excitation circuit 27 (power supply means) is a high frequency of 500 k Hz from 20 k Hz is to be generated by the switching power supply. The exciting coil 18 generates an alternating magnetic flux by the alternating current (high-frequency current) supplied from the exciting circuit 27.

The belt guide members 16a and 16b are substantially semicircular arc shaped cross-sectional members having a substantially cylindrical shape with their opening sides facing each other, and a cylindrical electromagnetic induction heating belt (electromagnetic induction heating member) on the outside. The fixing belt 10 is loosely fitted. The belt guide member 16a holds magnetic cores 17a, 17b, and 17c as magnetic field generating means and an excitation coil 18 on the inner side. Further, as shown in FIG. 4, the belt guide member 16a is provided with a good heat conducting member 40 in the longitudinal direction in the drawing as opposed to the pressure roller 30 in the nip portion N and inside the fixing belt 10. It is. In this example, aluminum is used for the good heat conducting member 40. The good heat conducting member 40 has a thermal conductivity k,
k = 240 [W · m-1 · K-1]
The thickness is 1 [mm].

  Further, the good heat conducting member 40 is disposed outside the magnetic field so as not to be affected by the magnetic field generated from the exciting coil 18 and the magnetic cores 17a, 17b, and 17c as magnetic field generating means. Specifically, the good heat conducting member 40 is disposed at a position separating the magnetic core 17c from the exciting coil 18, and is located outside the magnetic path by the exciting coil 18 to affect the good heat conducting member 40. I am trying not to. The pressurizing rigid stay 22 is a horizontally long stay disposed in contact with the inner surface flat portion of the belt guide member 16b. The insulating member 19 is a member for insulating the magnetic cores 17 a, 17 b, and 17 c and the exciting coil 18 from the pressurizing rigid stay 22. The flange members 23a and 23b are externally fitted to the left and right ends of the assembly of the belt guide members 16a and 16b, and are rotatably attached while fixing the left and right positions. As a result, the flange members 23a and 23b receive the end of the fixing belt 10 when the fixing belt 10 rotates, and serve to regulate the movement of the fixing belt 10 along the length of the belt guide member.

  The pressure roller 30 as a pressure member is composed of a core metal 30a and a heat-resistant / elastic material layer 30b made of silicon rubber, fluorine, fluorine resin, or the like that is concentrically formed and covered around the core metal 30a. It is configured. Both ends of the core metal 30a are rotatably supported between the chassis side metal plates (not shown) of the apparatus. By pressing the pressure springs 25a and 25b between the both ends of the pressure rigid stay 22 and the spring receiving members 29a and 29b on the apparatus chassis side, a pressing force is applied to the pressure rigid stay 22, respectively. . As a result, the lower surface of the belt guide member 16a and the upper surface of the pressure roller 30 are pressed against each other with the fixing belt 10 interposed therebetween, so that a fixing nip portion N having a predetermined width is formed.

  The pressure roller 30 is rotationally driven in the counterclockwise direction indicated by the arrow by the driving means M. A rotational force acts on the fixing belt 10 by a frictional force between the pressure roller 30 and the outer surface of the fixing belt 10 due to the rotational driving of the pressure roller 30. As a result, while the fixing belt 10 has its inner surface in close contact with the lower surface of the good heat conducting member 40 in the fixing nip portion N, it slides in a clockwise direction substantially corresponding to the rotational peripheral speed of the pressure roller 30. The belt guide members 16a and 16b are rotated around the outer periphery at a speed.

  In this case, in order to reduce the mutual sliding frictional force between the lower surface of the good heat conductive member 40 and the inner surface of the fixing belt 10 in the fixing nip portion N, the lower surface of the good heat conductive member 40 in the fixing nip portion N and the fixing belt 10. A lubricant such as heat resistant grease is interposed between the inner surface and the inner surface. Alternatively, the lower surface of the good heat conducting member 40 can be covered with a lubricating member. This is because, when the surface heat-slidability is not good as in the case of using aluminum as the good heat conducting member 40 or the finishing process is simplified, the sliding fixing belt 10 is damaged and the fixing belt 10 is damaged. This prevents the durability of the steel from being lowered.

  The good heat conducting member 40 has an effect of making the temperature distribution in the longitudinal direction uniform. For example, when small-size paper is passed, the heat amount of the non-sheet passing portion of the fixing belt 10 is transferred to the good heat conducting member 40, and the heat conduction in the longitudinal direction of the good heat conducting member 40 causes the non-paper passing portion to The amount of heat is transferred to the small size paper passing section. Thereby, the effect of reducing the power consumption at the time of passing small-size paper is also obtained. Further, as shown in FIG. 5, convex rib portions 16e are formed on the peripheral surface of the belt guide member 16a at predetermined intervals along the length thereof. Thereby, the contact sliding resistance between the peripheral surface of the belt guide member 16a and the inner surface of the fixing belt 10 is reduced, and the rotational load of the resistance belt 10 is reduced. Such convex ribs can be similarly formed on the belt guide member 16b.

  FIG. 6 is a diagram schematically showing how the alternating magnetic flux is generated. A magnetic flux C represents a part of the generated alternating magnetic flux. The alternating magnetic flux C guided to the magnetic cores 17a, 17b, and 17c is applied to the electromagnetic induction heating layer 1 of the fixing belt 10 between the magnetic cores 17a and 17b and between the magnetic cores 17a and 17c. Generate eddy currents. This eddy current causes Joule heat (eddy current loss) to be generated in the electromagnetic induction heat generating layer 1 by the specific resistance of the electromagnetic induction heat generating layer 1. The calorific value Q here is determined by the density of the magnetic flux passing through the electromagnetic induction heat generating layer 1 and shows a distribution as shown on the right side of FIG. The graph on the right side of FIG. 6 shows the circumferential position of the fixing belt 10 with the vertical axis represented by an angle θ with the center of the magnetic core 17 a being 0, and the horizontal axis is the electromagnetic induction heating layer 1 of the fixing belt 10. The calorific value Q is shown. Here, the heat generation region H is defined as a region where the heat generation amount is Q / e or more, where Q is the maximum heat generation amount. This is an amount by which a heat generation amount necessary for fixing can be obtained.

  The temperature of the fixing nip portion N is controlled so that a predetermined temperature is maintained by controlling the current supply to the exciting coil 18 by a temperature control system including a temperature detection unit (not shown). 2 in FIG. 2 is a temperature sensor such as a thermistor for detecting the temperature of the fixing belt 10. In this example, the temperature of the fixing nip N is controlled based on the temperature information of the fixing belt 10 measured by the temperature sensor 26. I am doing so.

  Thus, the fixing belt 10 is rotated, and the electromagnetic induction heat generation of the fixing belt 10 is performed as described above by the power supply from the excitation circuit 27 to the excitation coil 18, and the fixing nip portion N rises to a predetermined temperature and the temperature is adjusted. It becomes a state. In this state, the recording material P as the heated material on which the unfixed toner image t conveyed from the image forming unit is formed is positioned between the fixing belt 10 and the pressure roller 30 in the fixing nip N. Is introduced upward, that is, facing the surface of the fixing belt. In the fixing nip portion N, the image surface is in close contact with the outer surface of the fixing belt 10, and the fixing nip portion N is nipped and conveyed together with the fixing belt 10. In the process in which the recording material P is nipped and conveyed together with the fixing belt 10 through the fixing nip N, the unfixed toner image t on the recording material P is heated and fixed by being heated by electromagnetic induction heat generation of the fixing belt 10. Is done. When the recording material P passes through the fixing nip portion N, it is separated from the outer surface of the rotary fixing belt 10 and discharged and conveyed. The heat-fixed toner image on the recording material P is cooled to be a fixed image after passing through the fixing nip portion.

  In this example, as shown in FIG. 2, the thermoelectric sensor, which is a temperature detection element, is used to cut off the power supply to the exciting coil 18 at the time of runaway at a position opposite to the heat generating area H (see FIG. 6) of the fixing belt 10. A switch 50 is provided.

  FIG. 7 is a circuit diagram of the safety circuit used in this example. The thermo switch 50 that is a temperature detecting element is connected in series with the +24 VDC power source and the relay switch 51. When the thermoswitch 50 is turned off, the power supply to the relay switch 51 is cut off, the relay switch 51 is operated, and the power supply to the excitation circuit 27 is cut off to cut off the power supply to the excitation coil 18. The thermoswitch 50 was set to an OFF operating temperature of 220 degrees C. Further, the thermo switch 50 is disposed on the outer surface of the fixing belt 10 in a non-contact manner so as to face the heat generating area H of the fixing belt (film) 10. The distance between the thermo switch 50 and the fixing belt 10 was about 2 mm. As a result, the fixing belt 10 is not damaged by the contact of the thermo switch 50, and deterioration of the fixed image due to durability can be prevented.

  According to this example, when the fixing device runs away due to a device failure, the fixing device (fixing device) stops in a state where paper is caught in the fixing nip portion N, unlike the configuration in which heat is generated in the fixing nip portion N as in the conventional example. To do. As a result, even when power is continuously supplied to the exciting coil 18 and the fixing belt 10 continues to generate heat, the paper is not directly heated because no heat is generated in the fixing nip portion N where the paper is sandwiched. In addition, since the thermo switch 50 is disposed in the heat generating region H where the heat generation amount is large, when the thermo switch 50 senses 220 degrees C and the thermo switch 50 is turned off, the relay switch 51 switches to the exciting coil 18. Is interrupted. Further, according to this example, since the temperature at which the paper starts to burn is around 400 degrees C., the heat generation of the fixing belt 10 can be stopped without the paper starting to burn.

  In addition to the thermo switch, a temperature fuse can be used as the temperature detection element. In this example, since the toner containing the low softening material is used in the toner t, the fixing device is not provided with an oil application mechanism for preventing offset, but the toner containing no low softening material is used. May be provided with an oil application mechanism. In addition, when a toner containing a low softening substance is used, oil application or cooling separation may be performed.

<Excitation coil>
The exciting coil 18 is a conductive wire (electric wire) constituting a coil (wire ring) using a bundle of a plurality of copper thin wires each coated with an insulation coating (bundled wire). A coil is formed. As the insulating coating, it is preferable to use a coating having heat resistance in consideration of heat conduction due to heat generation of the fixing belt 10. For example, a coating such as amideimide or polyimide may be used. The excitation coil 18 may improve the density by applying pressure from the outside.

  The shape of the exciting coil 18 is made to follow the curved surface of the heat generating layer as shown in FIG. In this example, the distance between the heat generating layer of the fixing belt 10 and the exciting coil 18 is set to be approximately 2 mm. As the material of the exciting coil holding member 19, a material having excellent insulation and good heat resistance is preferable. For example, a phenol resin, a fluorine resin, a polyimide resin, a polyamide resin, a polyamideimide resin, a PEEK resin, a PES resin, a PPS resin, a PFA resin, a PTFE resin, an FEP resin, an LCP resin, or the like may be selected.

  When the distances between the magnetic cores 17a, 17b, and 17c and the heat generating layer of the fixing belt 10 are as close as possible, the magnetic flux absorption efficiency is higher. However, when the distance exceeds 5 mm, the efficiency is remarkably increased. In order to decrease, it should be within 5 mm. If the distance is within 5 mm, the distance between the heating layer of the fixing belt 10 and the exciting coil 18 does not have to be constant. With respect to the lead wires from the exciting coil holding member 19 of the exciting coil 18, that is, 18a and 18b (FIG. 5), an insulating coating is applied to the outside of the bundled wire for the portion outside the exciting coil holding member 19.

<Fixing belt>
FIG. 8 is an explanatory diagram showing the layer structure of the fixing belt 10 in this example. The fixing belt 10 of this example includes a heat generating layer 1 composed of a metal belt or the like as a base layer of an electromagnetic induction heat generating fixing belt 10, an elastic layer 2 laminated on the outer surface, and a release layer laminated on the outer surface. It has a composite structure with the layer 3. For adhesion between the heat generating layer 1 and the elastic layer 2 and adhesion between the elastic layer 2 and the release layer 3, a primer layer (not shown) may be provided between the respective layers. In the fixing belt 10 having a substantially cylindrical shape, the heat generating layer 1 is on the inner surface side, and the release layer 3 is on the outer surface side. As described above, when the alternating magnetic flux acts on the heat generating layer 1, an eddy current is generated in the heat generating layer 1 and the heat generating layer 1 generates heat. The heat heats the fixing belt 10 through the elastic layer 2 and the release layer 3, and heats the recording material P as a material to be heated that is passed through the fixing nip N to heat and fix the toner image. The

(A) Heat generation layer 1
The heat generating layer 1 may be made of a ferromagnetic metal such as nickel, iron, ferromagnetic SUS, or nickel-cobalt alloy. A non-magnetic metal may be used, but a metal such as nickel, iron, magnetic stainless steel, cobalt-nickel alloy, etc., which has good magnetic flux absorption is more preferable. The thickness is preferably thicker than the skin depth represented by the following formula and 200 μm or less. The skin depth σ [m] is the frequency f [Hz], the magnetic permeability μ, and the specific resistance ρ [Ωm] of the excitation circuit 27.
σ = 503 × (ρ / fμ) ^1/2
It is expressed.

  This indicates the depth of absorption of electromagnetic waves used in electromagnetic induction, and the intensity of electromagnetic waves is 1 / e or less deeper than this, and conversely most energy is absorbed up to this depth. (See FIG. 10). The thickness of the heat generating layer 1 is preferably 1 to 100 μm. If the thickness of the heat generating layer 1 is smaller than 1 μm, most of the electromagnetic energy cannot be absorbed and the efficiency is lowered. On the other hand, if the heat generating layer 1 exceeds 100 μm, the rigidity becomes too high, the flexibility is lowered, and it is not practical to use as a rotating body. Therefore, the thickness of the heat generating layer 1 is preferably 1 to 100 μm.

(B) Elastic layer 2
The elastic layer 2 is made of silicon rubber, fluorine rubber, fluorosilicon rubber, or the like, which has good heat resistance and good thermal conductivity. The depth of the elastic layer 2 is preferably 10 to 500 μm. The elastic layer 2 has a thickness necessary for assuring the fixed image quality. When a color image is printed, a solid image is formed over a large area on the recording material P, particularly in a photographic image. In this case, if the heating surface (release layer 3) cannot follow the unevenness of the recording material or the unevenness of the toner layer, heating unevenness occurs, and gloss unevenness occurs in the image where the heat transfer amount is large and small. A portion with a large amount of heat transfer has a high glossiness, and a portion with a small amount of heat transfer has a low glossiness. If the thickness of the elastic layer 2 is 10 μm or less, unevenness of the image gloss occurs because it cannot follow the unevenness of the recording material or the toner layer. On the other hand, when the elastic layer 2 is 1000 μm or more, the thermal resistance of the elastic layer 2 increases and it is difficult to realize a quick start. More preferably, the thickness of the elastic layer 2 is 50 to 500 μm.

If the hardness of the elastic layer 2 is too high, unevenness in image gloss will occur because it cannot follow the unevenness of the recording material or toner layer. Therefore, the hardness of the elastic layer 2 is preferably 60 degrees (JIS-A) or less, more preferably 45 degrees (JIS-A) or less. Regarding the thermal conductivity λ of the elastic layer 2,
6 × 10 ^{−4 to} 2 × 10 ⁻³ [cal / cm · sec · deg. ]
Is good.

The thermal conductivity λ is
6 × 10 ⁻⁴ [cal / cm · sec · deg. ]
Is smaller, the thermal resistance is large, and the temperature rise in the surface layer (release layer 3) of the fixing belt 10 is delayed.

The thermal conductivity λ is
2 × 10 ⁻³ [cal / cm · sec · deg. ]
If it is larger than 1, the hardness becomes too high, or the compressive strain decreases.

Therefore, the thermal conductivity λ is
6 × 10 ^{−4 to} 2 × 10 ⁻³ [cal / cm · sec · deg. ]
Is good. More preferably,
8 × 10 ^{−4 to} 1.5 × 10 ⁻³ [cal / cm · sec · deg. ]
Is good.

(C) Release layer 3
For the release layer 3, a material having good release properties and heat resistance such as fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA, PTFE, FEP can be selected. The thickness of the release layer 3 is preferably 1 to 100 μm. When the thickness of the release layer 3 is smaller than 1 μm, there arises a problem that a portion having poor release properties due to coating unevenness of the coating film is formed or durability is insufficient. Further, when the release layer 3 exceeds 100 μm, there arises a problem that the heat conduction is lowered. In particular, in the case of a resin release layer, the hardness becomes too high and the effect of the elastic layer 2 is lost.

  As shown in FIG. 9, in the configuration of the fixing belt (fixing film) 10, the heat insulating layer 4 may be provided on the belt guide surface side of the heat generating layer 1 (the side opposite to the elastic layer 2 of the heat generating layer 1). . The heat insulating layer 4 is preferably a heat insulating resin such as a fluororesin, a polyimide resin, a polyamide resin, a polyamideimide resin, a PEEK resin, a PES resin, a PPS resin, a PFA resin, a PTFE resin, or an FEP resin.

  Moreover, as thickness of the heat insulation layer 4, 10-1000 micrometers is preferable. When the thickness of the heat insulating layer 4 is smaller than 10 μm, the heat insulating effect cannot be obtained and the durability is insufficient. On the other hand, if the thickness exceeds 100 μm, the distance from the magnetic cores 17 a, 17 b, and 17 c and the exciting coil 18 to the heat generating layer 1 increases, and the magnetic flux is not sufficiently absorbed by the heat generating layer 1. Since the heat insulating layer 4 can insulate the heat generated in the heat generating layer 1 so as not to go to the inside of the fixing belt 10, the heat supply efficiency to the recording material P side is improved as compared with the case without the heat insulating layer 4. . Therefore, power consumption can be suppressed.

<High-frequency inverter device>
FIG. 1 is a block diagram showing an overall configuration of an induction heating control unit including an output converter shown in FIG. 12 described later in the image forming apparatus according to the first embodiment of the present invention. The induction heating control unit of the image forming apparatus according to the first embodiment of the present invention includes a voltage control circuit 300, a fixing unit unit (Fuser) 313, a feedback control circuit 315, and a driver circuit 316. Further, the voltage control circuit 300 includes a circuit breaker 302, a relay 303, a rectifier circuit (RECT) 304, gate control transformers 305 and 306, and a main switch element 307. Further, a second switch element 308, a resonance capacitor 309, a second resonance capacitor 310, and a current transformer 311 are provided. In the figure, 301 is a power line input terminal, and 314 is a heating ON / OFF signal input terminal of the fixing device.

  The configuration of the main part will be described in detail along with the operation. The circuit breaker 302 protects overcurrent. The rectifier circuit 304 includes a bridge rectifier circuit that performs both-wave rectification from an AC input and a capacitor that performs a high-frequency filter. The main switch element 307 and the second switch element 308 perform current switching. The current transformer 311 (current detection means) is a transformer that detects a switching current switched by the main switch element 307 and the second switch element 308. The fixing device unit 313 detects the temperature in the vicinity of the contact portion between the exciting coil 18 (FIG. 2) and the temperature detection thermistor 26 (FIG. 2) (the electromagnetic induction heating member and the material to be heated) as the electrical component configuration. Temperature detecting means) and a thermo switch 312 for detecting excessive temperature rise. The heating on / off signal input terminal 314 of the fixing device controls the output on / off of the high frequency inverter device by a voltage signal sent from a printer sequence controller of an image forming apparatus (not shown).

  The feedback control circuit 315 controls the control amount while comparing with the target temperature based on the thermistor temperature detection value of the fixing device (fixing device). The driver circuit 316 receives the feedback control signal from the feedback control circuit 315 and performs control suitable for the control mode of the high frequency inverter device. As the main switch element 307 and the second switch element 308, a power switch element for power is optimal, and is configured by an FET or IGBT (+ reverse conducting diode). Since the main switch element 307 and the second switch element 308 control the resonance current, the main switch element 307 and the second switch element 308 have a small loss during normal operation and a small switch loss, and preferably have a high breakdown voltage and a large current type.

  When AC power is received from the power line input terminal 301 and AC power is applied to the rectifier circuit 304 via the circuit breaker 302 and the relay 303, a pulsating DC voltage is generated by the double-wave rectifier diode of the rectifier circuit 304. . Thereafter, by driving the gate control transformer 305 so that the main switch element 307 performs switching, an AC pulse voltage is applied to the resonance circuit constituted by the excitation coil 18 and the resonance capacitor 309. As a result, a pulsating DC voltage is applied to the exciting coil 18 when the second switch element 308 is conductive, and a current determined by the inductance and resistance of the exciting coil 18 starts to flow. When the second switch element 308 is turned off according to the gate signal, the exciting coil 18 tries to continue to pass current. Therefore, a high voltage called a flyback voltage is generated at both ends of the excitation coil 18 due to the sharpness Q of the resonance circuit determined by the resonance capacitor 309 and the excitation coil 18. This voltage oscillates around the power supply voltage and converges to the power supply voltage if it is kept off as it is.

  During a period in which the ringback of the flyback voltage is large and the voltage at the coil side terminal of the second switch element 308 is negative, the reverse conducting diode is turned off and current flows into the exciting coil 18. During this period, the contact point between the exciting coil 18 and the second switch element 308 is clamped at 0V. It is generally known that if the second switch element 308 is turned on during such a period, the second switch element 308 can be turned on without carrying a voltage, and is called ZVS (Zero Voltage Switching). . With such a driving method, the loss associated with switching of the second switch element 308 can be minimized, and switching with high efficiency and low noise is possible.

<Current detector>
In the first embodiment of the present invention, an example will be described in which the current transformer 311 shown in FIG. 1 and FIG. 11 described later is used to detect the current flowing in the exciting coil 18 of the fixing device. An example of the detected waveform is shown in FIG. The current transformer 311 is configured to detect current flowing from the emitter (drain in the case of FET) of the second switch element 308 to the negative terminal of the rectifier circuit 304 and the filter capacitor (not shown) at the subsequent stage of the rectifier circuit 304. Yes. A current on the power side is passed through one turn side of a current transformer 311 having a 1: n winding, and is detected as voltage information by a detection resistor provided on the n turn side. The detected current is waveform-shaped by a filter circuit (passive filter) 319 (see FIG. 11 described later), and then a current peak is formed by a peak hold circuit 320 (see FIG. 11 described later) corresponding to a frequency of about 50 KHz. .

  Further, a current peak waveform including a voltage ripple is taken out by a peak hold circuit 340 (see FIG. 11 described later) corresponding to about 100 Hz connected next, and used as a maximum power control value. Specifically, a limiter operation is performed with this output voltage as a power control peak value. Further, the output waveform is input to the feedback control circuit 315 of FIG. 1 as a more stable voltage corresponding to the peak current by removing the ripple by the filter circuit 319 (see FIG. 11 described later) as the limit value of the maximum output power. Also good.

<Temperature control>
In the first embodiment of the present invention, as an example, temperature control is described as being performed by digital PID (Proportional plus Integral plus Derivative) control. The thermistor 26 detects the fixing temperature of the fixing device (fixing device). The thermistor 26 is disposed in pressure contact with the inner side of the sleeve at a portion corresponding to the downstream side of the fixing nip, and measures the amount of heat taken away by the paper as the material to be heated as a temperature change. The resistance change of the thermistor 26 is converted into a voltage by a detection circuit, and is detected as a difference from the target temperature (target voltage) by comparing it with a predetermined reference voltage. Based on the detection result, the ON time of the switch element is determined, and PWM (Pulse Width Modulation) control is performed.

  The PWM control circuit 323 is composed of two pairs of constant current source circuits, an on-time control unit and an off-time control unit, a capacitor, and a comparator. The time control is performed by exceeding the value. In order to prevent the elements other than the main switch element 307 from performing the on operation during the on time, the off time control unit is stopped during the on time, and the on time control unit is stopped during the off time. The on-time and off-time in which the time width is sequentially controlled by the output FF (steering flip-flop) 329 in the PWM control circuit 323 are repeatedly output. Although the off-time comparator can be adjusted, the power control is performed by changing the input voltage of the on-time comparator (not shown) to a fixed time by adopting a configuration without a feedback loop.

<Voltage dependence of maximum power>
The voltage dependence of the maximum power (initial power) will be described. In a system in which current control is not performed, the output power varies with the square of the AC line voltage relative to the AC line voltage. On the other hand, according to the present configuration in which a limit is set by current detection, the output power can be linearly dependent on the voltage. FIG. 14 shows the results of experiments performed by constructing such a circuit. The “non-control region” in FIG. 14A is an experimental result according to the conventional example, and the power fluctuation due to the power supply voltage is large. Is shown. The points indicated by square marks in FIG. 14B indicate the experimental results in the case of constant average current control, and the points indicated by diamonds indicate the experimental results in the case of constant peak control.

  Since the current is detected and the electric power is controlled, the maximum value of the time during which the current flows through the exciting coil 18 of the fixing unit 313, that is, the time during which the main switch element 307 is on can be supplied as the current flowing through the AC line. Determined by appropriate power. The control signal from the feedback control circuit 315 is in a range not exceeding the time. Moreover, you may take the structure which prescribes | regulates also about minimum time. For example, when the temperature of the fixing device of the image forming apparatus is low, such as when starting up an image forming apparatus such as a copying machine or a printer first in the morning, supply power with an on-time width close to the maximum time width. become. Assuming that the power that can be input is 1100 W as an example, 1100 W of power is supplied by current control within the range of the maximum on-time from when the power is turned on until temperature control is applied. The on-time width is limited as the temperature rises by a control method called PI control or PID control by a signal from the thermistor 26 that is a temperature detection element, and the power is controlled.

  When the temperature is sufficiently high and the on-time width is shortened by temperature control, the flyback voltage oscillates with the power supply voltage as the reference voltage as described above, so the power supply voltage is particularly high and the on-time width is short. In some cases, it cannot be reduced to 0V. Therefore, ZVS cannot be realized. In such a case, the circuit current detected by the current transformer 311 is compared with a reference value, and the second switch element 308 is driven. The second switch element 308 may be configured to continue normal operation.

FIG. 5 is a diagram showing a configuration in which the exciting coil 18 and the exciting circuit 27 are connected to generate an alternating magnetic field (magnetic field) by the exciting current. The excitation circuit 27 is constructed high-frequency inverter device as shown in FIG. 1, it generates a high-frequency current of about 20 k Hz 100 k Hz.

  FIG. 11 is a block diagram showing a detailed configuration of the excitation circuit 27 according to the first embodiment of the present invention. The exciting circuit 27 according to the first embodiment of the present invention includes a main switch element 201, a reverse conducting diode 202, an exciting coil 203, a resonant capacitor 204, and a second switch element 205. Furthermore, a reverse conducting diode 206, a second resonant capacitor 207, gate control transformers 305 and 306, a current transformer 311 and a switching control circuit 350 (emergency stop means) are provided. Further, the switching control circuit 350 includes a peak detection circuit 318, a filter circuit 319, a peak hold circuit 320, an operational amplifier 321, a rectifier circuit 317, a capacitor 341, and a resistor 342. Further, a PWM control circuit 323, a DC power supply 327, a capacitor 328, a switch element 330, resistors 331 and 332, diodes 334 and 335, and the like are provided.

  The switching control circuit 350 in the figure corresponds to the driver circuit 316 in FIG. In addition, the operational amplifier 321, the rectifier circuit 317, the capacitor 341, and the resistor 342 in the drawing constitute a second peak hold circuit 340. The main switch element 201, the second switch element 205, the excitation coil 203, and the resonance capacitors 204 and 207 in the figure are the main switch element 307, the second switch element 308, the excitation coil 18, and the resonance capacitor in FIG. 309 and 310 respectively. In the figure, reference numerals 333 and 336 denote terminals to which an instruction for urgently stopping the fixing operation by the fixing device installed in the image forming apparatus is input from the outside. Reference numerals 322, 324, 325, 337 and 338 in the figure denote signals. Is a line.

  The configuration of the main part will be described in detail along with the operation. Generally used as the main switch element 201 is an element such as a MOSFET or an IGBT. The configuration of the exciting coil 203 is as shown in FIGS. The reverse conducting diode 206 is connected in parallel to the second switch element 205. In a normal state, the second switch element 205 is in an open state, and single voltage resonance is performed by turning on and off the main switch element 201 in this state. The second switch element (sub-resonant switch element) 205 continues the above-described operation of turning on when the flyback voltage finishes rising and turning off when the voltage drops while the main switch element 201 is turned off. May be.

  The current flowing through the exciting coil 203 is detected by the current transformer 311, rectified by the rectifier circuit 317, and then detected by the filter circuit 319. This output is compared with a predetermined reference value by the peak detection circuit 318, and when it is detected that the peak current is equal to or greater than the reference value, the output FF (flip-flop) 329 of the PWM control circuit 323 is fixed to OFF and the output is Perform the limiter operation to be prohibited. Protection is performed in this way when an abnormal current is detected, such as when a large current flows. After the waveform shaping by the filter circuit 319, the peak hold circuit 320 first detects a peak at a high frequency (several tens of KHz), and the AC is used as an envelope of the commercial alternating current (commercial alternating current power supply) cycle connecting the current waveform peaks. The peak current flowing in the line is detected. A peak value corresponding to a commercial AC cycle is detected by a second peak hold circuit 340 including an operational amplifier 321, a rectifier circuit 317, a capacitor 341, and a resistor 342.

  In the first embodiment of the present invention, the maximum output value of the power control circuit is controlled based on the detected peak current. As a result, the maximum value (maximum power that can be applied) of the power control width is controlled based on the AC line current detection result, and the maximum power that can be supplied is controlled to be less dependent on the AC line voltage.

<Safety device>
The safety device is configured as follows. In this circuit configuration, AC power is received from the power input terminal 301 of FIG. 1 and is connected to the rectifier circuit 304 via a contact of a circuit breaker 302 and a relay 303 that protects eddy currents. Here, the excitation winding of the relay 303 is turned on by a 24V power source provided in the image forming apparatus. Further, the temperature of the fixing belt (film) 10 of the fixing device provided in the image forming apparatus is detected, and excitation is performed through a thermoswitch contact that shuts off when the detected temperature exceeds a specified temperature and abnormally increases. ing. If a trouble occurs and the fixing device abnormally increases in temperature, the power supply of the excitation circuit 27 is cut off via the relay 303 to protect the fixing device from thermal runaway.

The switching frequency is initially has a first street about 100 k Hz explained. In the initial state, the gate pulse width = 0, and the second switch element 205 (308) is not turned on. The gate pulse is output by the fixing start signal and increases to the duty determined by the current control circuit. At this time, if the limiter operates within half of the maximum on-time width, it is abnormal. It is determined that the information is notified to the outside.

  As described above, according to the first embodiment of the present invention, the fixing device that heats the material to be heated by the magnetic induction heating method includes the following configuration. A fixing unit unit 313 having an exciting coil 18, a fixing belt 10, and a thermistor 26. A current transformer 311 that detects a current flowing through the exciting coil 18. Control for limiting the maximum value of the power supplied to the excitation coil 18 based on the current detection value of the current transformer 311. When the detected temperature of the mutual pressure contact portion between the fixing belt 10 and the pressure roller 30 exceeds the specified temperature, the excitation coil A driver circuit 316 that performs control for stopping the power supply to 18. Thereby, there exist the following effects and effects.

  Maximum power control in the exciting coil 18 of the fixing device is performed using a signal from the current transformer 311. As a result, when the metal fixing belt 10 is heated by the magnetic induction heating fixing method, the maximum power is maintained at a constant value, the output reduction due to the temperature rise is eliminated, and a faster and more stable on-demand fixing is realized. There is a possible effect. Further, when the detected temperature of the mutual pressure contact portion between the fixing belt 10 and the pressure roller 30 exceeds a specified temperature, the power supply to the exciting coil 18 is stopped, and the fixing operation (heating operation) is urgently stopped based on an external input. It is possible. As a result, the fixing device can be protected from thermal runaway, and an emergency stop of the fixing operation in an emergency can be achieved.

[Second Embodiment]
FIG. 15 is a block diagram showing a detailed configuration of the excitation circuit 27 according to the second embodiment of the present invention. The exciting circuit 27 includes a main switch element 201, a reverse conducting diode 202, an exciting coil 203, a resonant capacitor 204, a second switch element 205, and a reverse conducting diode 206. Further, a second resonant capacitor 207, gate control transformers 305 and 306, a current transformer 311 and a switching control circuit 360 (control means) are provided. Further, the switching control circuit 360 includes a rectifier circuit 317, a peak detection circuit 318, a first filter circuit 345 (first filtering means), a second filter circuit 346 (second filtering means), an operational amplifier 347, and PWM control. A circuit 323 is provided. Further, a DC power supply 327, a capacitor 328, a switch element 330, resistors 331 and 332, diodes 334 and 335, and the like are provided. The description of the overlapping part with FIG. 11 in the first embodiment is omitted.

  The switching control circuit 360 in the figure corresponds to the driver circuit 316 in FIG. Further, the main switch element 201, the second switch element 205, the exciting coil 203, the resonance capacitor 204, and the second resonance capacitor 207 in the figure correspond to the following parts. That is, it corresponds to the main switch element 307, the second switch element 308, the exciting coil 18, the resonance capacitor 309, and the second resonance capacitor 310 of FIG. In the figure, reference numerals 333 and 336 denote terminals to which an instruction for urgently stopping the fixing operation by the fixing device installed in the image forming apparatus is input from the outside. Reference numerals 322, 324, 325, 337 and 338 in the figure denote signals. Is a line.

  The configuration of the main part will be described in detail along with the operation. The current flowing through the exciting coil 203 is detected by the current transformer 311, rectified by the rectifier circuit 317, and then detected by the first filter circuit 345. This output is compared with a reference value determined in advance by the peak detection circuit 318. When it is detected that the peak current is equal to or greater than the reference value, the output FF 329 of the PWM control circuit 323 is fixed off, and a limiter operation for prohibiting the output is performed. It is the structure to perform (prohibition means). Abnormal current detection and circuit protection are performed in this way when a large current flows through the circuit.

  After the waveform of the current is shaped by the first filter circuit 345, filtering at a lower frequency is performed by the second filter circuit 346, the current is detected as an average current flowing in the AC line, and an average current value (average) is obtained by the operational amplifier 347. The voltage corresponding to the current value is output. This output voltage is used as a control power supply voltage for the current control circuit. As a result, the maximum value of control width (maximum power that can be applied) is controlled based on the AC line current detection result (so that the maximum current flowing through the magnetic field generating means is limited), and the maximum power that can be supplied is AC line voltage. Control is performed in proportion to

The switching frequency is initially has a first street about 100 k Hz explained. In the initial state, the gate pulse width = 0, and the second switch element 205 (308) is not turned on. The duty is increased by duty control. At this time, if the limiter operates within half the maximum on-time width, it is determined to be in an abnormal state and notified to the outside. Yes.

  As described above, according to the second embodiment of the present invention, similarly to the first embodiment, the maximum power control in the excitation coil 18 of the fixing device is performed using the signal of the current transformer 311. . As a result, when the metal fixing belt 10 is heated by the magnetic induction heating fixing method, the maximum power is maintained at a constant value, the output reduction due to the temperature rise is eliminated, and a faster and more stable on-demand fixing is realized. There is a possible effect. In addition, the fixing device can be protected from thermal runaway, and an emergency stop of the fixing operation in an emergency can be achieved.

[Third Embodiment]
FIG. 16 is a block diagram showing a detailed configuration of the excitation circuit 27 according to the third embodiment of the present invention. The exciting circuit 27 includes a main switch element 201, a reverse conducting diode 202, an exciting coil 203, a resonant capacitor 204, a second switch element 205, and a reverse conducting diode 206. Further, a second resonant capacitor 207, gate control transformers 305 and 306, a current transformer 311 and a switching control circuit 370 are provided. Further, the switching control circuit 370 includes a rectifier circuit 317, a peak detection circuit 318, a filter circuit 351, a first peak hold circuit 352, a second peak hold circuit 353, and a PWM control circuit 323. Further, a DC power supply 327, a capacitor 328, a resistor 332, diodes 334 and 335, a switch element 353, and the like are provided. The description of the overlapping part with FIG. 11 in the first embodiment is omitted.

  The switching control circuit 370 in the figure corresponds to the driver circuit 316 in FIG. Further, the main switch element 201, the second switch element 205, the exciting coil 203, the resonance capacitor 204, and the second resonance capacitor 207 in the figure correspond to the following parts. That is, it corresponds to the main switch element 307, the second switch element 308, the exciting coil 18, the resonance capacitor 309, and the second resonance capacitor 310 of FIG. In the figure, reference numerals 333 and 336 denote terminals to which an instruction for urgently stopping the fixing operation by the fixing device installed in the image forming apparatus is input from the outside. Reference numerals 322, 324, 325, 337 and 338 in the figure denote signals. Is a line.

  The configuration of the main part will be described in detail along with the operation. The peak current information obtained by passing through the first peak hold circuit 352 and the second peak hold circuit 353 is converted into a digital signal by the A / D converter built in the circuit 315 to the feedback control circuit 315 (FIG. 1). Converted and transmitted. The result is input as peak current information to a PID control unit built in the circuit 315 that performs temperature control, and the maximum power that can be supplied is controlled so that the maximum power converted therefrom does not exceed a certain value. The calculation result is reflected as gate-on time information to be output to the gate pulse signal, and is input to the switching control circuit 370 as a voltage output from the D / A converter from the CPU built in the circuit 315 or a PWM output.

  When the calculation result exceeds the maximum power, the maximum power calculated from the peak current information is output, and the PID control data is also smoothed by feeding back the actual output power width instead of the calculation result. It is configured so that it can be controlled. When it is necessary to apply the current limiter operation as a safety circuit different from the control loop for each wave, the first embodiment applied in hardware may be used as it is.

  As described above, according to the third embodiment of the present invention, the maximum power control in the excitation coil 18 of the fixing device is performed using the signal of the current transformer 311 as in the first embodiment. . As a result, when the metal fixing belt 10 is heated by the magnetic induction heating fixing method, the maximum power is maintained at a constant value, the output reduction due to the temperature rise is eliminated, and a faster and more stable on-demand fixing is realized. There is a possible effect. In addition, the fixing device can be protected from thermal runaway, and an emergency stop of the fixing operation in an emergency can be achieved.

[Other embodiments]
In the first to third embodiments described above, the type of image forming apparatus on which the fixing device of the present invention is mounted is not particularly mentioned. The present invention can be applied to various image forming apparatuses such as a copying machine and a printer that perform image formation by heating and fixing an unfixed image as a fixed image on a heated material.

  In the first to third embodiments described above, the configuration other than the image forming apparatus on which the fixing device of the present invention is mounted is not particularly mentioned. The present invention may be applied to a system constituted by a plurality of devices such as an image forming apparatus or an apparatus constituted by a single device such as an image forming apparatus.

FIG. 2 is a block diagram illustrating a configuration of an induction heating control unit of the fixing device of the image forming apparatus according to the first exemplary embodiment of the present invention. 1 is a cross-sectional view illustrating a structure of a main part of a fixing device of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a configuration diagram with a part in cross section showing a front structure of a main part of the fixing device of the image forming apparatus according to the first embodiment of the present invention. 1 is a cross-sectional view showing a front structure of a main part of a fixing device of an image forming apparatus according to a first embodiment of the present invention. 1 is a perspective view showing a belt guide member, an excitation coil, and the like constituting a fixing device of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is an explanatory diagram showing a state of generation of alternating magnetic flux in a fixing belt or the like of the fixing device of the image forming apparatus according to the first embodiment of the present invention. 1 is a circuit diagram showing a safety circuit of a fixing device of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a schematic cross-sectional view illustrating an example of a layer configuration of a fixing belt of the fixing device of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 6 is a schematic cross-sectional view illustrating another example of the layer configuration of the fixing belt of the fixing device of the image forming apparatus according to the first exemplary embodiment of the present invention. It is explanatory drawing which shows the relationship between the electromagnetic wave intensity | strength which concerns on the 1st Embodiment of this invention, and a heat generating layer depth. 2 is a block diagram illustrating a detailed configuration of an excitation circuit of the fixing device of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. FIG. 2 is a circuit diagram illustrating a configuration of an output converter of the fixing device of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 6 is an explanatory diagram illustrating an example of a current detection waveform in the fixing device of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 6 is a diagram showing an experimental result of maximum power dependency in the fixing device of the image forming apparatus according to the first embodiment of the present invention, where (a) shows the power in the case of the non-control region and the constant peak control region. (B) is a power-voltage characteristic in the case of constant current constant control and constant peak control. 6 is a block diagram illustrating a detailed configuration of an excitation circuit of a fixing device of an image forming apparatus according to a second embodiment of the present invention. FIG. FIG. 10 is a block diagram illustrating a detailed configuration of an excitation circuit of a fixing device of an image forming apparatus according to a third embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fixing belt 18 Excitation coil 26 Thermistor 27 Excitation circuit 30 Pressure roller 301 Power line input terminal 302 Circuit breaker 311 Current transformer 315 Feedback control circuit 316 Driver circuit 318 Peak detection circuit 345 First filter circuit 346 Second filter circuit 347 Operational amplifier 351 Filter circuit 352 First peak hold circuit 353 Second peak hold circuit

Claims (1)

A magnetic field generating means for generating a magnetic field, a power supply means for supplying power to the magnetic field generating means connected to an AC input power source, an electromagnetic induction heating member for generating electromagnetic induction heat by the action of the magnetic field generated from the magnetic field generating means, Temperature detection means for detecting the temperature of the electromagnetic induction heating member; and control means for controlling the power supplied from the power supply means to the magnetic field generation means so that the temperature detected by the temperature detection means becomes a target temperature. In an image forming apparatus that includes a heating device of an electromagnetic induction heating method having a heating and fixing an unfixed image on a material to be heated by the heating device,
Current detection means for detecting a current supplied to the magnetic field generation means;
Filtering means for detecting the current detected by the current detection means as an average current value,
The control means keeps the average current value detected by the filtering means constant so that the maximum power that can be supplied to the magnetic field generation means changes linearly with respect to fluctuations in the voltage of the AC input power supply. Limiting the maximum current flowing through the magnetic field generating means,
An image forming apparatus, wherein power supplied from the power supply unit to the magnetic field generation unit is controlled within a range not exceeding the maximum power so that the detected temperature becomes the target temperature.

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